When changing such rolls one normally uses rail systems with whose help the rolls are shifted with their bearing mounts through the mount windows of the rolling-mill frame. These rails and the equipment used for such an operation take a great deal of space up at the roll frame and make it difficult to mount or move other equipment needed for rolling.
It has therefore been suggested to change rolls by means of a support beam, a so-called porter bar. To this end the stub of the roll is connected to a porter bar suspended from a crane, and the roll is lifted in this position out of the frame. With this method there is the problem that the bearing mount rotates on the roll as it is being moved.